In a typical telescope, a number of lenses and/or mirrors are arranged along a light path to gather and focus light rays onto an image surface The image size and character may be describe in part in terms of an entrance pupil (sometimes termed “pupil” herein) at the entrance aperture, the telescope magnification, and imager behind the telescope to focus the light. The optical components are enclosed in a package structure that supports and aligns the optical components, and protects them from damage. One goal of the design of many imaging optical systems is to obtain satisfactory optical performance in as small a volume, in as short a physical length, and with as low a total weight, as possible. The physical length, of the package is particularly important for many applications, which can have tight physical length limitations.
In most cases, the physical length of the imaging optical system is several times the diameter of the entrance pupil. To reduce the physical length, and thence the volume and weight of the imaging optical system, the lenses and/or mirrors may have higher optical power (i.e., greater curvatures), and an associated greater numerical aperture, as compared with more-conventional lenses and/or mirrors. Such higher optical power lenses and their imaging optical systems are therefore more sensitive to fabrication and alignment errors. The production yield of such components and systems is typically relatively low, and costs are therefore higher, when using the higher-optical-power lenses and/or mirrors to achieve a compact imaging optical system.
There is a need for a compact imaging optical system that achieves good optical performance with reduced physical length, volume, and weight as compared with the known imaging optical systems, but does not require the use of high-optical-power lenses and/or mirrors with their associated high production costs. The present invention fulfills this need, and further provides related advantages.